What is the meaning of Harden?

To become hard.

To make something hard or harder.

To strengthen.

To modify (a website or other system) to make it resistant to malicious attacks.

To become or make (a person or thing) resistant or less sensitive.

To get an erection.

To become or make (a consonant) more fortis; to (cause to) undergo fortition.

To unpalatalize or velarize.

Alternative form of hurden (coarse linen)

to render hard(er), more resistant etc.; to temper metal; to steel nerves

to endure, bear, stand, tolerate

plural of harde

Source: wiktionary.org